1. Field of the Invention
This invention relates to a method for producing thin plate ingot of phosphor bronze by the quench-solidification method.
2. Description of Background
As the method for producing ingot of phosphor bronze, there has so far been practiced generally a continuous casting by means of a horizontal continuous casting apparatus. As an example, FIG. 5 of the accompanying drawing is a schematic cross-sectional view showing a conceptual structure of the conventional horizontal continuous casting apparatus as disclosed in Japanese Unexamined Patent Publication No. 38639/1983. In the drawing, a reference numeral 1 designates melt of a metal which has been molten by, for example, a melting furnace (not shown in the drawing) operated by electric power such as high frequency electromagnetic waves, and so forth; a numeral 2 refers to a holding furnace for maintaining the melt in its constant state and quantity; a numeral 3 refers to a graphite mold fixedly provided at the lower end part of the holding furnace; a reference numeral 4 denotes a water-cooling jacket provided on and around the graphite mold in a manner to surround the same; and a reference numeral 5 represents traction rollers to draw out an ingot 6 which has resulted from the melt 1 due to its cooling and solidifying.
In the casting apparatus of the above-described construction, the melt 1 which has been stored in the holding furnace 2 is poured into the graphite mold 3 and becomes solidified under the cooling effect of a cooling water which flows in an through a water passageway formed in the interior of the water-cooling jacket 4, and is finally taken out of the mold 3 in the form of the ingot 6. At that time, the ingot 6 is drawn out by the traction rollers either intermittently or continuously, whereby a long, continuous ingot 6 is obtained. After this, the ingot is subjected to repeated rolling and annealing processes to be finished into a thin plate having a predetermined size.
FIG. 6 of the accompanying drawing is a micrograph (magnification: 50 times) of a metal structure of the ingot 6, in its cross-section, obtained by casting the melt 1 having a composition of 8% by weight of Sn, 0.15% by weight of P, and a balance of Cu, in accordance with the above described casting method.
FIG. 7 of the accompanying drawing is a graphical representation showing changes in density of Sn in relation to cutting distance from the surface of the above-mentioned ingot, the analysis of Sn being effected by use of the fluorescent X-ray at a position where the surface of the ingot has been cut.
Further, FIG. 8 of the accompanying drawing is a graphical representation showing distribution in density of Sn as analyzed by an electron probe microanalyzer (EPMA) in the cross-section of the above-mentioned ingot.
From these results of analyses, it can be verified that the ingot obtained by the conventional method indicates a columnar crystal structure having the dendritic structure as shown in FIG. 6, that a surface segregation of Sn appears as shown in FIG. 7, and that density of Sn within the crystal structure varies conspicuously as shown in FIG. 8. Accordingly, in order to improve its roll-processability which is the essential requirement for producing a long web of thin plate product, it has been indispensable to subject the ingot to a homogenizing heat-treatment at a high temperature and for a long period of time to thereby render uniform the density of Sn for effecting the necessary processing. On account of this, the annealing and rolling processes have to be done until such time the ingot is finished to a predetermined size, which inevitably consumes a great deal of energy for the manufacture of the thin plate product.